1. Field of the Invention
This disclosure is related to applications of very high Q cryogenic dielectric resonators at X-band to the development of ultra low phase noise phase noise sources for radar.
2. Description of the Related Art
X-hand dielectric resonators using low order TE.sub.On modes and higher order whispering gallery modes of a sapphire puck are being developed to work at temperatures ranging from room temperature to cryogenic temperatures. Because the loss tangent of sapphire varies as the fifth power of temperature, lowering the operating temperature to .about.77 K (liquid nitrogen) allows Q values of .about.10.sup.6 (low order modes), and &gt;10.sup.7 (high order modes) to be realized. To realize the full Q potential at cryogenic temperatures, low loss puck support posts must contact the puck at the center of the flat faces. The resonant electric field amplitudes in and around the puck near the z axis are very small and a post aligned along the z axis will have minimal effect on resonant frequency and resonant Q.
One of our earlier spindle (post) mount sapphire resonators was made out of a single piece of c-axis sapphire. The solid sapphire-puck is contained within a metal cavity as shown in FIGS. 1a and 1b and was designed for TE.sub.02 operation at 10 Ghz. The measured Q of this resonator at 77 K was 0.6.times.10.sup.6, where we expected 1.0.times.10.sup.6. The Q degradation was due to a low quality finish of the flat faces of the puck. These faces could not be properly finished with the spindle in the way. For the next phase of the STALO program we ordered sapphire puck and separated post sets where all faces of the puck had a high quality finish. These pucks were dimensioned for higher order whispering gallery mode operation at X-band because the Q requirements (10.sup.7) of this phase of the program could not be satisfied with TE.sub.On modes.